Introduction Review of experimental results on π + - K + K - CF
Analysis of the D + s K + K - π + channel in the ALICE experiment
description
Transcript of Analysis of the D + s K + K - π + channel in the ALICE experiment
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Analysis of theD+
s K+K -π+ channel in the ALICE experiment
Serhiy SenyukovUniversità & INFN di Torino
(4050 m. asl)
Open charm and QGP
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QGP
A
A
c
Ds
K
K
πD0
π
K
Primary producti
on
Interaction with QGP
Decay of D
mesons
Detection of
products
c-
Results for D0 and D+
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2<pT<3 GeV/c
p-p @ 14 TeV
Pb-Pb @ 5.5TeV
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Question: We know that D0 and D+ can be reconstructed with
high significance. Why do we need also Ds?Answer:1. To measure charm yield more precisely we need to
measure as many channels as we can2. Study of different ways of hadronization:
• String fragmentation:Ds+ (cs) / D+ (cd) ~ 0.6it should be easier to take a light meson from a vacuum than the strange one
• Recombination:Ds+ (cs) / D+ (cd) ~ N(s)/N(d) (~ 1 at
LHC?)recombination occurs inside the medium.
Why Ds?
ALICE setup
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Inner Tracking System:
Vertexing, Tracking,PID
Time Projection Chamber:Tracking,
PIDTime-of-Flight
detector:PID
Selection strategy
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invariant-mass analysis of fully-reconstructed
topologies originating from displaced vertices
build triplets of tracks with correct combination of charge signs and large
impact parameters particle identification to tag
the decay products calculate the vertex (DCA
point) of the tracks good pointing of
reconstructed D momentum to the primary vertex
Primary Vertex
Ds flight line
Secondary vertex
K
K
DsKK
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Ds vs. D+ & D0
D0 D+ Ds
Combinations * 106 pairs 109 triplets 108 triplets
cτ 123 μm 312 μm 150 μmHadronic branching
ratio3.8% 9.2% 4.3%
Abundance** 30 9 5* - without cuts, with Ideal PID at dη/dy=6000** - PbPb (0-5% central), NLO pQCD + Binary Scaling + EKS98, in central acceptance
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Cut tuning schemeSignal events
Cuts alghoritms
Background events
Cuts alghoritms
Normalization to 107 events
Normalization to 107 events
Significance calculationSignif=S/(S+B)1/2
Significance normalized
o Signal – 2500 PYTHIA events with full simulation each containing 9100* Ds generated in the barrel acceptance (-0.9<η<0.9) forced to decay into hadronic channels:
o D+sK+K0*K+K -π+
o D+sφπ+K+K-π+
o Background – 15000 HIJING(Number of signal is negligible)
o Significance – calculated with respect to 107 central events (1 year) * Number is tuned in order to have the
same performance of the detector as in BKG event
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Single track selection3 variables:• Pt(K) – Transverse
momentum of Kaon*• Pt(π) – Transverse
momentum of Pion*• d0 – impact parameter of
track
Before cuts After cuts
Cut: Pt>0.5 GeV/cCut: Pt>0.5 GeV/cCut: d0>35 μm
* Ideal PID is assumed
Pt of Ds (GeV/c)
Pt of Ds (GeV/c)
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Combining tracks to pairs• Single tracks are combined to pairs with opposite sign (K+K- &
K+π-) or (K-K+ & K-π+)• Crossing point is found using vertexing algorithm• Two values are calculated:
– Dispersion of tracks around the cross-point:– Distance from cross-point to primary vertex
• First cut is made on dispersion: σ<300 μm• Second cut is made on the distance: d(pair)<300 μm
22 2 2 2
1
( ) ( ) ( )k o k o k ok
x x y y z z
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Triplet selection• Triplet of 3 tracks is
formed• Secondary vertex is
calculated• Dispersion of tracks
around the vertex is found• Cuts are tuned in for Pt bins:
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Resonances separation• Ds decays via resonances• Calculation of Inv Mass for KK and Kπ
pairs• Accept triplet if
|M(KK)-m(φ)|<Δm1 OR |M(Kπ)-m(K0*)|<Δm2
Inv
Mas
s (K
π)
Inv Mass (KK)
Inv
Mas
s (K
π)
Inv Mass (KK)
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Final multicutVariables considered:1. Cos Θpoint2. Cos Φopening3. Distance between primary and secondary vertex4. Sum of impact parameters squared5. Dispersion of secondary vertex (additional
tuning)
Signal Ds via φ
Signal Ds via K0* K0*-like BKG
φ-like BKG
Cos Point
Cos Opening
D+s
π+
K+
K-Φopeni
ng
Pt(Ds)
Θpoin
t
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Results for Ideal PID
φ K0*
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Conclusion and To-Do•Monte-Carlo simulation shows that reconstruction of the
DsKKπ is feasible in the range of Pt down to 3 GeV/c.
•Study of Real PID is in progress. Reduction of significance by factor of ~2 is expected
•Bigger statistics for background events is needed to reduce the error and better tuning of cuts.
•Case of pp collisions is under study. Some preliminary results without multicut are present.
3-5 GeV/c
>5 GeV/c
φ channel 5.1±0.4 19±5K0*
channel 2.0±0.7 9±3